This disclosure relates to power distribution systems for electric vehicles.
Battery-powered vehicles commonly use batteries to supply both a high output voltage for powering the vehicle and low output voltages for operating various computers, lights, electric fans, and other low-power systems on board the vehicle. To provide the low voltage to the on-board systems, the batteries often include a voltage converter to convert the high output voltage to a lower voltage. The low-voltage power output of vehicle batteries is often a small fraction of the nominal power output of the battery. Because the amount of time the batteries operate in low-voltage modes can be very long, it is desirable for voltage converters to operate efficiently to reduce loss of energy stored in the batteries. However, the efficiency of voltage converters decreases as the difference between the input voltage and the output voltage increases.
To improve efficiency in low voltage modes, power systems for battery-powered vehicles may include an auxiliary battery having a suitable voltage output for operating the on-board systems without a converter. If the efficiency of a voltage converter for the high-voltage propulsion batteries drops below a threshold value, the auxiliary battery is used to supply power to the on-board systems. The auxiliary battery may be charged by the voltage converter of the high-propulsion batteries. However, an auxiliary battery represents a single point of failure for the power systems of the electric vehicle. A second auxiliary battery and voltage converter may be added to the power system to provide redundancy, but this redundancy adds weight to the vehicle.